Elbow dysplasia is a significant problem in many dog breeds worldwide. It is common in some large breeds such as the Bernese Mountain Dog, German Shepherd, Golden Retriever, Labrador, Newfoundland, Rottweiler and others. ED can start in puppy hood and affect the dog for the rest of its life.
Put very simply, ED means ‘abnormal development of the elbow.’ ED includes three major specific abnormalities that affect different sites within the elbow joint. These abnormalities are the primary cause of ED which then induce a secondary osteoarthritic process:
- Osteochondritis dessicans (OCD)
- Fragmented or ununited medial coronoid process (FCP)
- Ununited anconeal process (UAP)
The elbow joint is like a hinge in which bones and cartilage on each side of the joint have complex shapes that should fit closely together. The elbow has a wide range of joint movement and the normal gait of the foreleg is dependent on it. Even a small change in the shape of one part of the joint can have major consequences for its function.
A complication of ED is that a large proportion of dogs with ED are subclinical. This means that they have the joint lesions but do not appear lame. If two such dogs are mated together they can produce offspring which are seriously affected.
Elbow dysplasia, like hip dysplasia, is a polygenetic trait which means that it is controlled by the combination of many genes. How many of these genes a dog inherits determines the severity of the disease in an individual dog. Environmental factors such as diet and exercise can influence the severity of the disease in an individual dog but ED has high heritability.
Due to its complex nature there is no genetic test for ED but the BVA/KC run a screening scheme whereby the elbows are radiographed (x-rayed) for signs of ED. Two radiographs of each joint are taken and a grade is then calculated for each elbow. The overall grade is determined by the higher of the two individual grades (unlike hip dysplasia).
0 = Normal
1 = Mild ED
2 = Moderate ED or a primary lesion
3 = Severe ED
Ideally dogs with ‘normal’ elbows should be used for breeding and dogs graded 2 or 3 should never be used.
The success of screening depends on a high proportion of a breed participating and making the information public so that low risk animals can be selected for breeding. Unfortunately as with the Hip Dysplasia scheme the scheme for ED is voluntary. Untested dogs are allowed to be bred as are those with poor ED scores. And as with HD, progress towards eliminating this painful disease is painfully slow.
Estimated Breeding Values (EBVs)
One advantage of the BVA/KC scheme is that over the years a huge amount of data has been collected by the Animal Health Trust (AHT) which can now be used to calculate estimated breeding values for ED in those breeds which have participated in the scheme in sufficient numbers.
The breeds for which EBVs are available for ED are:
Labrador, German Shepherd, Bernese Mountain Dog, Golden Retriever, Rottweiler
EBVs are a more accurate way of measuring a dog’s genetic risk, than by using the scores from the BVA/KC scheme alone. EBVs take into consideration a dog’s elbow score as well as the scores of all their relatives. A dog’s EBV is either a positive or negative number with the breed average set at zero. A negative number means the dog has a lower genetic risk of disease than the breed average. A positive number indicates a higher than average risk of disease. By using all the data in a dog’s pedigree, EBVs are available for all KC registered dogs (of the above breeds) regardless of whether the dogs themselves have been elbow scored. Each EBV is accompanied by a confidence value which ranges from 0 to 100. The EBV is an estimate of each dog’s genetic risk for a condition, while the confidence value shows how close to the dog’s true genetic risk the EBV is likely to be. The more data from the BVA/KC scheme that is available from an individual’s pedigree, the more accurate the EBV will be and the more confidence there is in the estimate of genetic risk. EBVs are not an alternative to elbow scoring as the scores provide the data on which the EBVs are based. The EBVS become more accurate as more data is provided. EBVs mean that greater improvements can be made in selecting dogs for breeding.
Carol Fowler April 2014